1. Field of the Invention
The present invention relates to a coating apparatus, and a coating method, which perform a coating process of applying a resist liquid or the like to a substrate, such as a semiconductor wafer or an LCD substrate (glass substrate for liquid crystal display), and a coating process for a developing liquid after exposure, and the like, and, more particularly, to a technique for substrate transfer by means of substrate transfer means.
2. Description of the Related Art
One of fabrication processes for a semiconductor device or an LCD substrate is a sequence of processes of acquiring a desired pattern by forming a resist film on a substrate, exposing the resist film using a photomask, then performing a developing process. Such a sequence of processes is generally carried out by using a resist pattern forming apparatus that has an exposure apparatus connected to a coating and developing apparatus which applies and dries a resist liquid. One example of such an apparatus is disclosed in Unexamined Japanese Patent Application KOKAI Publication No. 2002-050668. In the apparatus, as shown in, for example, FIG. 1, a carrier 10 retaining multiple wafers W is carried onto a carrier stage 11 of a carrier block 1A, and the semiconductor wafers W (hereinafter called “wafers W”) in the carrier 10 are transferred to a process block 1B by a transfer arm 12. A sequence of processes for forming a resist film is executed by a coating unit 13A, etc. in the process block 1B, and then the wafers are transferred to an exposure apparatus 1D via an interface block 1C.
The wafers after exposure are returned to the process block 1B again to undergo a developing process in the developing unit 13B, after which the wafers are returned to the original carrier 10. Referring to FIG. 1, reference numerals 14A to 14C denote shelf units comprising heating units (HP, PEB, POST), cooling units (CPL1 to CPL4), a transfer stage (TRS) and so forth for performing a predetermined heating process and cooling process on wafers before and after the processing of the coating unit 13A and the processing of the developing unit 13B.
In the apparatus, the wafers W are transferred between modules, in the process block 1B, where the wafers W are to be placed, such as individual sections like the coating unit 13A, the developing unit 13B and the shelf units 14A to 14C, by a main arm 15 provided in the process block 1B. At the time wafers W are subjected to the processes, all the wafers W to be processed are transferred according to a transfer schedule that specifies at which timing each wafer is to be transferred to which module, as indicated by the technology disclosed in the aforementioned Unexamined Japanese Patent Application KOKAI Publication No. 2002-050668. In FIG. 1, reference numeral 16 is an interface arm which transfers a wafer W between the process block 1B and an exposure apparatus 1D.
FIG. 2 is an explanatory diagram illustrating a transfer path of wafers W in this system. The transfer mechanism 12 serves to transfer an unprocessed wafer W in a carrier 10, placed on the carrier stage 11, to a transfer unit (TRS), and transfer a processed wafer W, undergone development and placed on a cooling unit (CPL4), to the carrier 10. The main transfer mechanism 15 serves to transfer wafers W on the transfer unit (TRS1) to a cooling unit (CPL1), a coating unit (COT), a heating unit (HP), and a cooling unit (CPL2) in that order, and further transfer wafers W, carried out of the interface block 1C and placed into the heating unit (PEB), to a cooling unit (CPL3), a developing unit (DEV), a heating unit (POST), and a cooling unit (CPL4) in that order.
The main transfer mechanism 15, as shown in FIG. 3, for example, has three arms 15a, 15b, and 15c provided in an advanceable and retreatable manner along, for example, a base 17, and the base 17 is so configured as to be liftable up and down rotatable about the vertical axis by a lifting mechanism and a rotating mechanism, which are not shown. The configuration is such that after a wafer W placed in a preceding unit is received by, for example, one arm 15b, a wafer W placed in a next unit is received by the other arm 15c, and the wafer W placed on the one arm 15b is transferred.
At this time, between the main transfer mechanism 15 and a cooling unit (CPL1-CPL4), and a heating unit (HP, PEB, POST), the arm 15b, 15c enters a unit and transfers a wafer W therebetween, so that at the time of receiving a wafer W from a heating unit, the arm itself is heated, and the temperature rises.
When a wafer W is received from the cooling unit (CPL1) in the preceding step of the coating unit (COT) and is transferred to the coating unit (COT) using the heat-accumulated arm, heat is transferred to the wafer W cooled by the cooling unit (CPL1), raising the temperature of the wafer W during transfer, thus deteriorating the in-plane uniformity of the wafer temperature. The wafer temperature at the time of coating significantly influence the film thickness, so that when the wafer temperature changes during transfer, the in-plane uniformity of the film thickness depends on the temperature change and becomes lower.
Conventionally, therefore, one arm 15a in the main transfer mechanism 15 is provided as an exclusive arm for transfer of a wafer W to the coating unit (COT) from the cooling unit (CPL1), and a wafer W is transferred to the coating unit (COT) from the cooling unit (CPL1) using other arms whose temperatures do not change, there by suppressing a change in temperature during transfer of a wafer W cooled by the cooling unit (CPL1) and improving the in-plane uniformity of the film thickness. However, the arm 15a is not used in ordinary transfer and is not frequently used, and such an arm 15a with a low frequency of usage requires a drive system. This lowers the cost performance and stands in the way of reducing the cost of the apparatus. The use of three arms this way lead to enlargement of the main transfer mechanism.